Machines such as, rope shovels typically include an implement, such as a dipper, for loading and unloading materials. The dipper may include a door that closes a rear of the dipper to hold the materials that are loaded into the dipper. Further, the door is opened to unload the contents of the dipper at a desired location. The door may be typically held closed by a latch mechanism. The latch mechanism may be released to allow the door to swing open under its own weight and the weight of the contents of the dipper. The door may be re-latched as the door rotates back in preparation for its next loading cycle.
During the swinging movement, the door may tend to hit against walls of the dipper or any other proximal component. Sudden opening and closing of the door may also damage components associated with the door. Typically, dippers may be equipped with a braking device on the door linkage to reduce a swing speed as the door swings towards an open and/or closed position.
Conventional dipper door braking devices may utilize a dry friction to provide a braking force. As the door swings open or closed by virtue of its own weight, the braking device provides friction thereby reducing the swing speed of the door. However, the braking force provided by the braking device tends to reduce as the braking device wears. To maintain the necessary braking force, the braking devices may be subjected to regular maintenance, resulting in machine downtime.
An example of another conventional dipper door braking device can be found in U.S. Pat. No. 4,286,693 (hereinafter referred to as the '693 patent). The '693 patent discloses a mechanical, seismic-shock-absorbing snubber adapted to accept extremely high impact loads that may be imposed upon it by reason of its interposition between heavy, relatively moveable structures. The snubber of the '693 patent employs an escapement wheel as its damping mechanism. The wheel rotates in response to a relative movement of the structures between which the snubber is interposed and employs a cooperating, pivoted, pallet member of predetermined effective mass driven by the escapement wheel into oscillation. It is the oscillation of the pallet member, the rate of which is limited by the pallet member's mass and natural period of oscillation that restricts or damps the velocity and acceleration of relative motion between the structures with which the snubber is associated.